Nepheline

Nepheline, a mineral silicate of alumina, soda, and potash, crystallising in hexagonal prisms, generally clear, colourless, and glassy, but small.' Its hardness is 5-5 to 6; its specific gravity 2-5 to 26.

It derives its name from the Greek nephele, "a cloud," because it becomes cloudy on immersion in nitric acid before gelatinising. It is fusible. Nepheline is an essential constituent of phonolite (q.v.), and occurs also in other lavas.